Hydraulic-electrical apparatus for automatically regulating the position of direct arc electric furnace electrodes



Filed July 16, 1952 P 2, 1953 w. VOKAC ET AL 2,653,269

C. HYDRAULIC-ELECTRICAL APPARATUS FOR AUTOMATICALLY REGULATING THE POSITION OF DIRECT ARC ELECTRIC FURNACE ELECTRODES 2 Sheets-Sheet 1 FIG. I

INVENTO CHARLES W. VOKA EZ GEORGE M. ROTHENBERGER WOODRUFF A. MOREY sYW// ATTORNE Filed July 16, 1952 Sept. 22, 1953 c. w. VOKA ET AL 2,653,269

. HYDRAULIC-ELECTRICAL APPAR TUS FOR AUTOMATICALLY REGULATING THE POSITION OF DIRECT ARC ELECTRIC FURNACE ELECTRODES 2 Sheets-Sheet 2 I4 2 la 57 FIG. 4

' NVEN CHARLES V0126 GEORGE M. ROTHENBERGEP WOODRUFF A. MOREY ATTORNE I connected to the electrodes.

Patented Sept. 22, 1953 HYDRAULIC-ELECTRICAL APPARATUS FOR AUTOMATICALLY REGULATING THE PO- SITION OF DIRECT ARC ELECTRIC FUR- NACE ELECTRODES Charles W. Vokac, Cicero, George M. Rothenberger, Harvey, and Woodrulf A. Morey, Park Forest, 111., assignors to Whiting Corporation, a corporation of Illinois Application July 16, 1952, Serial No. 299,294

Claims.

This invention refers to hydraulic-electrical apparatus for automatically regulating the position of direct are electric furnace electrodes in such manner as to maintain the arc current and voltage substantially at predetermined levels.

Direct are electric furnaces usually utilize three movable electrodes connected to a suitable three phase transformer, the electrodes being supported in an upright position by horizontal electrode arms extending across the roof of the furnace. The electrodes extend downwardly through the furnace roof into close proximity with a charge of metal in the furnace hearth and are moved upwardly and downwardly by suitable mechanism coupled to the electrode arms, the latter being suitably supported in guides for vertical movement. In some instances this movement is accomplished by cable and Winch devices coupled to the arms, and in other instances by hydraulic piston and cylinder assemblies, the latter being considered preferable due to their greater responsiveness. Downward movement of the electrode is accomplished by Withdrawing fluid from the hydraulic cylinder,

allowing the electrode arm and electrode to move downward by gravity, reverse movement being accomplished by the introduction of liquid into the cylinder.

During operation of the furnace, the condition of the arc circuit through each electrode varies abruptly, thus necessitating rapid movement' of the electrode to compensate for the change in circuit condition and return the circuit to the desired condition. Inadequate and improper response of the electrode may result in breaking of the arc, dipping the electrode into the molten metal, or shorting the arc circuit for excessive periods.

There are available conventional control devices for signaling changes in the condition of the arc circuit, these signals being amplified and transmitted to the motors and pumps or winches The response of the system to such a signal is, however, not instantaneous, due to the inertia inherent in such devices, with the result that there is a considerable lag between the generation of such a signal and responsive movement of the electrode. The signaling devices currently employed, while satisfactory in some respects, are relatively expensive and complex.

An important object of this invention is to provide automatic electric-hydraulic electrode position control :means for direct are electri furnaces adapted for quickly changing the position of the electrode in response to a variation in the condition of the arc circuit with only a minimum of delay due to inertia and other causes.

Another important object of this invention is to provide apparatus of the type described which is easily adjusted and relatively inexpensive, highly responsive, durable, efficient, and which moves the electrode at a rate proportional to the degree of variation of the arc circuit from normal.

A further important object of this invention is to provide improved electrical signaling means for controlling the electrode positioning means on a direct are electric furnace.

()ther important objects, as Well as the many advantages of this invention, will be disclosed in the course of the following description and in the appended drawings, in which:

Fig. 1 is the diagrammatic elevation of an electric furnace illustrating the hydraulic electrode positioning apparatus;

Fig. 2 is a partial diagrammatic illustration of a modified form of hydraulic electrode positioning device;

Fig. 3 is a partial diagrammatic illustration of another modified form of hydraulic electrode positioning device;

Fig. 4 is a circuit diagram of a suitable electric control system for use with the hydraulic electrode positioning apparatus;

Fig. 5 is a circuit diagram of a modified form of control apparatus, and

Fig. 6 is a circuit diagram of another form of electrical control apparatus for use with the hydraulic electrode positioning apparatus.

In brief, this invention contemplates use of two electrically driven positive displacement hydraulic pumps disposed between the hydraulic electrode positioning cylinder and a fluid accumulator or reservoir. One of the pumps constantly forces fluid from the accumulator into the cylinder, while the other of the pumps constantly withdraws fluid from the cylinder and discharges into the accumulator. The electrode is elevated by allowing the rate at which fluid is discharged into the cylinder to exceed the rate at which fluid is discharged therefrom, the reverse action occurring when the cylinder is lowered. This variation in the effective rates of pump discharge is accomplished by varying the speed of either or both of the unidirectional motors coupled to the pumps. In its simplest form, a constant speed motor is coupled to a small pump which discharges fluid into the cylinder. A shunt wound direct current motor having a constantly energized field is coupled to a second pump of somewhat larger capacity which withdraws fluid from the cylinder. The armature of the direct current motor is energized through a current rectifier by the secondary of atransformer, the primary of which is connected across the are between the electrode and furnace ground. Variation in the are thus varies the armature current of the direct current motor and increases or decreases the discharge rate of the second pump through a range which includes a point at which the volume discharges of the pumps are equal. As subsequently described, both motors may be made to vary oppositely in speed from the same signal, which increases the responsiveness of the system.

It will be noted that it is not necessary at any time to reverse the direction of rotation of either pump or motor. As a result, the delay of inertia usually encountered between transmission of the signal requiring a change of electrode position and the response of the electrode to such a signal is reduced. The rate at which the pumps respond to such signals is directly proportional to the strength of such signals which is in turn directly proportional to the degree of variation in the condition of the arc circuit. As a result, the rate of electrode movement is proportional to the variation in the arc circuit.

It will be understood that a complete hydraulic system and electrical control system is applied to each of the furnace electrodes. For simplicity, only one such system will be described, it being understood that three such units would be required to control the three electrodes of a three phase direct arc furnace.

Referring to Fig. l, a conventional electric furnace shell I is lined with a refractory II and adapted to receive an electrically conductive charge, indicated at l2. A conventional ground rod l3 having a lead l4 extends through the shell Ill and refractory II into electrical contact with the charge I2. A roof l6 extends over the shell l8 and is provided with an opening I! for an upright electrode l8 of carbon or graphite. A generally horizontal electrode arm l9 supports the electrode [8 and a bus 2|, the latter being connected electrically to the electrode I8 and to flexible conductors 22, which communicate with the secondary of a power transformer 23. Variable impedance devices 25 of conventional design are inserted on either the primary or secondary side of the transformer 23 to limit and control the transformer. An upright channel 24 is coupled to the arm l3 and is mounted for generally vertical movement between rollers 28 rotatably carried by a bracket 21 on the shell III. A ram cylinder 28 is supported within the channel 24 and is reciprocally sealed around a ram 29, the exposed end of which engages the channel 24 or the electrode arm is in such manner that upward movement of the ram 23 forces the arm I8 and electrode 3 upwardly.

An accumulator 3| is provided with an air inlet valve 32, a liquid outlet 33 and a liquid inlet 34. The outlet 33 is connected to a check valve 38 and to a second check valve 31, the former communicating with the inlet of a suitable positive displacement rotary liquid pump 38. The specific design of the positive displacement pump 38 is not critical and may suitably be either of the gear type or the vane type as desired. The outlet of the pump 33 communicates via a con uit 39 with an inlet 4| in the cylinder 28. An outlet 42 for the cylinder 28 communicates with a conduit 43, which in turn communicates with the inlet of a spring loaded check valve 44, the outlet of the check valve 31 and with an inlet for a rotary positive displacement liquid pump 46 similar to pump 38. The outlet side of the spring loaded check valve 44 communicates with the accumulator inlet 34 and with the discharge side of a second spring loaded relief valve 41, the inlet of which communicates with the outlet of the pump 46.

Referring to Fig. 4, a transformer 48 has a primary winding 49 connected to one of the conductors 22 as close to the electrode [8 as possible and to the lead l4 for the ground rod l3, thus placing primary winding 49 in shunt connection across an are formed between the electrode i8 and the charge I2. The secondary winding 5| of the transformer 48 is connected to a rectifier 52, the output of which is connected to an armature 53 of a direct current motor gen erally designated as 54, preferably of the type having a shunt field winding 56. A variable resistor 51 is disposed in the output circuit of the rectifier 52 for varying the current flowing through the armature 53. The field winding 56 is preferably energized from a suitable constant source of direct current. The motor 54 is coupled directly to the pump 46 and rotates in such direction as to withdraw liquid from the cylinder 23, discharging into the accumulator 3|. A constant speed alternating motor 58 is coupled to the pump 38 and rotates continuously at a substantially constant speed in such direction as to continuously force liquid from the accumulator 3| into the cylinder 28.

Although not essential in all instances, air under pressure can be introduced into the accumulator 3| through the valve 32, the relief valves 44 and 41 being then adjusted to prevent flow of liquid from the cylinder 28 into the accumulator 3| when the pumps 38 and 46 are not running. Usually, the pressure of the air in the accumulator 3| should be suificient to only partially counterbalance the weight of the electrode [8 and arm IS. The electrode l8, at the initiation of furnace operation, is held above the charge l2 until the pumps 38 and 46 are placed in operation by energizing the motors 54 and 58. The output of the pump 46 under operating onditions should ordinarily be approximately twice the output of the pump 38, in order that it be able to overcome the effect of the pump 38 when motor 54 is operating at maximum speed. As the circuits to the electrode [8 and the motors 54 and 58 are first closed, there is no are between the electrode 18 and the charge l2. Primary winding 49 of the transformer 48 will therefore receive maximum energization with the result that the full output of the recifier 52 is passed through the armature 53. Since the shunt winding 56 is already energized, the motor 54 will be driven at maximum speed. thus driving the pump 46 at such rate that its discharge substantially exceeds the discharge of the pump 38, which is driven at a constant speed by the motor 58. Liquid discharged by the pump 46 is forced through the relief valve 41 into the accumulator 3| for recirculation. Operation of the pump 46 under these conditions withdraws liquid from the cylinder 28, allowing the electrode to move downwardly at a rapid rate. At the moment the electrode |8 contacts the charge l2 the resistance between the electrode and the charge l2 falls to virtually zero, with the result that the current available to the primary 49 of the transformer 48 is substantially reduced. This reduces the current flowing to the armature 53, thus quickly reducing the motor speed and allowing the pum 38 to drive the ram 29 upwardly, thus drawing an are between the electrode I8 and the charge I2. As the arc is drawn, the current flowing through the primary winding 49 gradually increases, which increases the speed of the motor 54 until the arc has reached the desired length. at which time the discharge of the pump 46 will be equal to the discharge of the pump 38. Should the are break or fail to strike, motor 54 will quickly accelerate, thus again lowering the electrode and striking or re-establishing the arc. The operator can select the desired arc length by the manipulation of the resistor 51, which increases or decreases the speed of the motor 54.

Maintaining rotation of the motors 54 and 58 under virtually all operating conditions imparts to the device certain highly desirable characteristics. For example, when the motor is running, greater toroue is available for effecting a change of speed. Also, the effectof slip or minor leakage in the pump is inconsequential. Since neither motor is at any time reversed, the undesirable friction and hydraulic phenomena experi enced in passing such a rotating system through a stationary or motionless condition are avoided.

It will be noted that the function of the motor 58 and the pump 38 which it drives are to supply liquid under pressure at a constant rate to the cylinder 23. It is therefore possible to substitute for the pump 38 and motor 58 an orifice 59 (Fig. 3), provided pressure of air in accumulator 3| is maintained substantially constant and suificient for forcing liquid into the cylinder 28 at the desired rate. A valve 5! may be interposed between the orifice 58 and the cylinder 28 blocking iiow of fluid through the orifice. In this form of device the pump 38 is driven by motor as previously described, and discharges into the accumulator 3| preferably through the spring loaded relief valve 41. Should th power supply fail, the electrodes will be automatically raised.

The speed of a direct current shunt wound motor may be varied and will increase within limits as the current to the armature is increased from a low initial point. W eakening the field of such a motor will also increase the motor speed, assuming constant armature energization. It is therefore possible, as illustrated in Fig. 5, to utilize a constant speed alternating motor 62 connected to the pump 46 for driving the electrode I8 downwardly, and a variable speed motor 53 coupled to the pump as for driving the electrode upwardly. The motor 53 in this instance is preferably a shunt wound direct current motor having an armature s4 connected through a suitable variable resistor 65 to a constant source of direct current. The transformer 48, as in l, energizes rectifier 52 but in this instance the rectifier 52 is constructed in such manner as to have an output voltage equal only to approximately 50 per cent of that needed to fully energize a field winding 57 for the motor $3. The output of rectifier 52 is therefore connected in series with the field winding 67 and with a second rectifier 58 having a substantially equal voltage output but constantly energized from a suitable source. Under such circumstances the voltage output of the rectifiers 52 and 68 are added and when fully energized combine to supply the necessary maximum voltage of the field Winding 61. g

In operation, primary winding 49 of the transformer 48 will be fully energized when no arc exists between electrode I8 and the charge it. Under such circumstances the output voltage of the rectifier 52 will be at a maximum, thus supplying in combination of this output of the rectifier 68 full energization to the field winding 57 of the motor 63 and holding this motor at its normal speed. The pump 46, driven by the motor 62, will thus be suiiicient to move electrode is downwardly at the desired rate. As the electrode I8 contacts the charge I 2, the energization of the transformer 48 will be greatly reduced, thus re ducing the output of the rectifier 52 and weakening the field 62'. This permits the motor (is to increase its speed, thus raising the electrode i 8 and drawing the arc. The energization of the field winding 6'! varies only between limits, the lower limit being fixed by the output of rectifier 68.

Again it will be noted that the motor 52 driving the pump 45 serves only to discharge liquid into the accumulator 3| at a constant rate. An orifice 69 (Fig. 2) may therefore be substituted for the motor 62 and pump 46 if desired, it being understood that under such circumstances the pressure of air in the accumulator 3I is suitably reduced to permit the flow of fluid from the cylinder 28 to the accumulator 3| through the orifice 69. A valve 'II may be interposed between the orifice 69 and the cylinder 28 to check the flow of oil if desired. Pump 33 is, of course, coupled under such circumstances to the motor the latter being energized as indicated in Fig. 5, and discharging through the spring loaded relief valve "J2 similar to valve 41.

I It has been demonstrated that the variation in the output of the transformer '38 may be made to increase or decrease the speed of a suitable direct current motor. It is also possible, as illustrated in Fig. 6, to utilize the output of the transformer .48 to accomplish both of these effects simultaneously in two motors, thereby still further increasing the speed of response of the system. As indicated in Fig. 6, the output of rectifier 52 is connected in series with a suitable source of direct current such as a constantly energized recti fier 58, the combined voltages of the two recti. 2 being sufficient to energize a field winding "8 for a D. C. shunt wound motor M- to its maximum degree, the winding 13 being inserted in series between the rectifiers 98 and 52. The motor is is coupled to pump 38 (Fig. 1), and utilizes an armature '56 connected across wire "1?, which connects rectifier 52 with. rectifier and wire 18 which connects rectifier 68 with the field winding 13. The pump 46 is connected to a D. C. shuntwound motor 19 having a shunt field winding BI in series with the armature Id. The armature 82 of the motor TS is connected across the wire Ti and a wire 83, the latter connecting field winding :3 with the rectifier 52. A variable resistor 84 may be inserted in the circuit to the armature 32 for speed control.

I When no arc exists between armature I8 and the charge I 2 and the transformer 43 is fully energized, the maximum current will flow to the armature 82 of the motor 79 as well as to the field 13 of the motor 14. The speed of the motor 19 will therefore be at a maximum while the speed of the motor I4 is at a minimum, thus moving the electrode I3 downwardly at the desired maximum speed. As the electrode I8 contacts the charge I2 the output of the rectifier 52 is reduced, which not only reduces the current flowing to the armature 82, slowing down the motor 19, butv accepts also weakens the ifield 13 "which increases the speed-of the motor '14, thus driving the electrode upwardly as in p-revious'instances. Operation of 'therh'eostat 84 by the operator controls position of the-electrode IB with respect to charge 1 2.

In the various modifications described it will be noted that a relationship must exist between the discharge volumes of 'the two pumps employed under various conditions, always including an intermediate condition in which the dis-- charge volumes are equal. This can be obtained by various expedients. For example, referring again to Fig. l, the pump 38 is driven at a constant speed by the motor 58 and therefore has a. predetermined discharge volume to move the electrode downwardly. The discharge volume of the pump 4Gimust be capable of exceeding the discharge volume of the pump 38 and to move the "electrode upwardly thevolume of the pump 46 must fall below the discharge volume of the pump 38. If the motors 54 and 58 operate at the same normal maximum speeds, then the capacity 'of the'p'ump 46 should be approximately twice the capacity of the pump 38, thus requiring the motor .54 to operate at only half of the normal speed to hold the electrode substantially motionless. If the pumps 46 and 3B are of the same capacity, then the normal maximum speed of the motor 54 driving pump 46 under the conditions described "should be approximately twice the normal maximum speed of the motor 58. It will also be understood that other conventional flows of voltage regulating devices may be substituted for the variable resistors. For example,

variable auto-transformers may be employed for this purpose in either the input or output circuits of the potential control transformers or substituted therefor.

The type of variable speed motor employed is not critical, although shunt wound direct current motors are generally most satisfactory. Compound wound or series wound motors may be substituted but in so doing certain potentially undesirable characteristics are unnecessarily added.

Furthermore, it will be noted that the control system herein described is applicable also to single and two phase electric furnace circuits.

From the foregoing it will be apparent to those skilled in the art that apparatus has been provided which to a marked degree attains the objectives of this invention. The sensitivity and high rate of response of the apparatus are effect'ive in substantially reducing the violent current surges to which furnace electrode circuits are normally subject, not only in magnitude, but also in frequency and duration, resulting in a far more suitable and satisfactory circuit condition. The cost of the apparatus to perform these functions has been reduced appreciably and the apparatus simplified, the latter being reflected in reduced maintenance costs. The efficiency of the furnace is, of course, increased for various reasons including the ability of the control system to maintain the desired are under virtually all circumstances. The improved electrode position control also permits better metallurgical control by avoiding clipping of the electrodes in the molten metal, and also prolongs the life of the refractory linings through better regulation of the heat developed by the arcs.

We claim:

1. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap, conductor means for supplying electric current "to the electrode and telescopic liquid confining means coupled to the electrode for varying electrode position, the improvement which includes first means ro'r forcing 'liquid into the confining rneans, second "means in nydraulic's'e"ries withthe "first means for withdrawing liquid "troi'n th'e confining means, one of said first a;hd 'secohd means "comprising a positive displacement hydraulic pump and pump control means responsive tova 'r ia'tions in the arcing gap varying the pump 'dischai-ge volume through a range including an intermediate point at which the volume discharge of the first means equals the volume discharge or the second means.

*2. In a'n electric are tneltin'g furnace of the type 'having an electrode movable for varying the arcing gap, conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying electrode position, the improvement which includes first liquid metering means hav'-- ing an outlet, second liqui'd metering means having 'an inlet communicating "with the outlet for said first means, both said inlet and said outlet communicating with the liquid confining means, one of said firstand second metering-means comprising a rotary .positive displacement hydraulic pump and pump control means responsive to variations in the arcing gap varying the pump discharge volume through a range including an intermediate point at which the volume discharge of the first means equals the volume discharge of the second means.

3. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap, conductor means 'for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying electrode position, the improvement which includes first liquid "metering means having an outlet, second liquid metering 'means having an inlet communicating with the outlet for said first means, both said inlet and said outlet communicating with the liquid confining means, one of said first and second means comprising a positive displacement hydraulic pump having a rotatable driving shaft and a unidirectional variable speed electric motor coupled to said driving shaft and control means responsive to variations in the arcing gap of the electrode varying the speed of said motor and thereby the discharge volume of the pump through a, range including an intermediate point at which the volume discharge of the first means equals the volume discharge of the second means.

4. The structure defined in claim 3 wherein the other of said first and second means comprises an orifice and means maintaining the vol-- utrnetdischarge of such orifice substantially con"- s an 5. The structure defined in claim 3 wherein the other of said first and second means comprises a second rota-ry positive displacement pump and a substantially constant speed motor coupled to said second pump.

6. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap, conductor means for supplying elec tric current to the electrode and telescopic liquid confining means coupled to the electrode for varying electrode position, the improvement which includes first liquid metering means havme an outlet, second liquid metering means having an inlet communicating with the outlet for said first means,'both said inlet and said outlet communicating with the liquid confining means, said'first and second liquid metering means comprising first and second rotary-positive displacement ,pumps, each coupled respectively to jfirst and second motors,'the speed of said motorsbeing variable-through arange including an intermediate point at which the volume dischargeof the first pump is equal to the volume discharge of the second pump, and motorspeedicontrol means responsiveto variations in ,thearcing gap of the electrode for simultan'eously increasingthe speed of one motor .andidecreasing the speed of theother motor.

7.,In an electric are melting furnaceof the type having an electrode movable for varying the arcing gap, conductor means for supplying electric current to ,the electrode and telescopic liquid confining meanscoupledto the electrode for varying electrode position, theirnprovement which. includesfirst. means for, forcing liquid, into said confining means, second means in, hydraulic series with the first means-for withdrawing gliqdid from the confiningrmeans, one of-said first and second means comprising apositive displacement hydraulic pump, a, transformer having a primary winding connected between the electrode and furnaceground, avariable; speed motor coupled to said pump and-energized by, said transformer, the speed of said motorvarying withthe transformer output and through a range including an inter-mediateispeed iat-which the discharge volume of the firstmeans equals the discharge volume of thesecond means.

8. In an electricarc melting :furnace of the type having an electrode movable for varying the arcing gap between the electrode and a grounded charge, conductor means f0r.supp1ying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying the electrode position, the improvement which includes a first positive displacement pump having an outlet, a second positive displacement pump having an inlet communicating with the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, one of said motors being a variable speed direct current motor and means responsive to variation in the arcing gap varying the speed of said motor through a range including an intermediate point at which the discharge volumes of said pumps are equal, said last mentioned means including a transformer connected between the electrode and furnace ground and a rectifier connected between the transformer and the variable speed motor.

9. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap between the electrode and a grounded charge, conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for Varying the electrode position, the improvement which includes a first positive displacement pump having an outlet, a second positive displacement pump having an inlet communicating with the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, one of said motors being a direct current motor'having an armature and a field, a substantially constant current sourceconnected to the field and variable armature current Supply means responsive to variations in the arcing gap for varying the speed of said motor and thereby the discharge volume of the pump through a range including an intermediate point at which the discharge volumes of saidpumps are equal. 7

10. In an electric arc melting furnace of the it pehaving an electrode movable for varying the arcing gap between the electrodeand a grounded charge, conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varyingth'e-electrode position, the improvement ,WhlGh includes a fir stpositive displacement pump having an outlet, a second positive displacement pump having an inlet communicating with the ,Qutlet of the first u both said inlet and said outlet communicating with a the liquid confining means, liquid supply means for thefirst pump, first and second motors coupled respectively to thefirst and second pumps, one of said motors being a directcurrentmotor having an armature and a field, asubstantially constant current source for said-armature and variable field current supply means responsive to-variations in the arcing gap for varying-the speed of said motor and thereby the discharge volume of, the pump through arange including an intermediate point at which, the discharge volumes of said pumps are equal.

11. In an electric arc-melting furnace of the type having an electrode movable for varying the arcing gap between the electrode and grounded charge, conductor means for supplying electric current to the electrode and telescopic liquid confiningmeans coupled to the electrode for varying the electrode position, the improvement which includes a first positive displacement pump having an outlet, a second positive displacement pump having an inlet communicating with the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, one of said motors being a direct current motor having an armature and a field, a substantially constant current source connected to the field and variable armature current supply means responsive to variations in the arcing gap for varying the speed of said motor and thereby the discharge volume of the pump through a range including an interme diate point at which the discharge volumes of said pump are equal, said variable armature current supply means include a transformer connected between the electrode and furnace ground and a rectifier connected between the transformer and said armature.

12. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap between the electrode and a grounded charge, conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying the electrode position, the improvement which includes a first positive displacement pump having an outlet, a second positive displacement pump having an inlet communicating With the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, one of said motors being a direct current motor having an armature and a field, a substantially constant current source for said armature and variable field current supply means responsive to variations in the arcing gap for varying the speed of said motor and thereby the discharge volume of the pump through a range including an intermediate point at which the discharge volumes of said pumps are equal, said variable field current supply include a transformer connected between the electrode and furnace ground and a rectifier connected between the transformer and said field.

13. In an electric arc melting furnace of the type having an electrode movable for varying the arcing gap between the electrode and a grounded charge, conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying the electrode position, the improvement which includes a first positive displacement pump having an outlet, a second positive displacement pump having an inlet communicating with the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, both of said motors having direct current field and armature windings, a substantially constant current source connected to the field of the first motor and to the armature of the second motor and a variable control current source connected with the armature of the first motor and the field of the second motor, said control current being variable responsive to variation in the arcing gap for simultaneously varying the speeds of said motors inversely through a range including an intermediate point at which the output volumes of said pumps are equal.

14. In an electric arc melting furnace or the type having an electrode movable for varying the arcing gap between the electrode and a grounded charge, .conductor means for supplying electric current to the electrode and telescopic liquid confining means coupled to the electrode for varying the electrode position, the improvement which includes a first positive dis-- placement pump having an outlet, a second positive displacement pump having an inlet communicating with the outlet of the first pump, both said inlet and said outlet communicating with the liquid confining means, liquid supply means for the first pump, first and second motors coupled respectively to the first and second pumps, both of said motors having direct current field and armature windings, a substantially constant current source connected to the field of the first motor and to the armature of the second motor, a variable control current source connected to the armature of the first motor and to the field of the second motor and means for maintaining a predetermined minimum energi zation of the field of said second motor, said control current being variable responsive to variation in the arcing gap for varying the speeds of said motors inversely through a range including an intermediate point at which the output volumes of said pumps are equal.

15. The structure defined in claim 13 in which the variable control current source includes a transformer having a primary winding connected between the electrode and furnace ground, a secondary winding and a rectifier energized by the said secondary.

CHARLES W. VOKAC. GEORGE M. ROTHENBERGER. WOODRUFF A. MOREY.

No references cited. 

